Known torque transmission systems comprise a gearbox having a gearbox housing and a gearbox input shaft, a wet clutch arrangement having a housing arrangement which is filled or fillable with fluid, a first friction surface formation which is rotatable around an axis of rotation with the housing arrangement, and a second friction surface formation which is rotatable around the axis of rotation with a driven element, the housing arrangement has a hub region which engages in a shaft opening of the gearbox housing, is rotatably supported so as to be substantially fluid-tight with respect to the gearbox housing by means of a bearing/seal arrangement, and encloses the gearbox input shaft, and a fluid pump for supplying fluid to an interior space of the housing arrangement and a fluid reservoir for receiving fluid removed from the interior space of the housing arrangement are provided in the gearbox housing.
In a torque transmission system of the type mentioned above, the gearbox is in fluid exchanging communication with the wet clutch arrangement; fluid is conveyed into the interior space of the housing arrangement of the wet clutch arrangement during torque transmitting operation by the fluid pump or oil pump arranged in the gearbox, can flow around the friction surface formations therein, and is then removed from the interior space again and fed back into a fluid pan or oil pan formed in the gearbox housing for further recirculation. Because of this fluid exchanging connection existing between the gearbox and the wet clutch arrangement, the interior space of the housing arrangement gradually empties in direction of the gearbox over a longer period of disuse; fluid flows back into the gearbox from the interior space until reaching the lowest point of the fluid exchange connection in vertical direction. This lowest point generally lies in the region of the height level of the gearbox input shaft so that it can be assumed in general that approximately one half of the interior space of the housing arrangement will no longer be filled with fluid after a longer period of disuse. This can have a disadvantageous effect on subsequent restarting.
It is an object of the present invention to provide a torque transmission system, particularly for a vehicle, in which restarting problems caused by a gradual emptying of fluid from a wet clutch arrangement are prevented.